Methods and apparatus for use in the manufacture of innerspring assemblies

ABSTRACT

An apparatus is provided for applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which apparatus comprises a plurality of independently actuatable adhesive applicators, each having a different transverse position relative to a longitudinal axis of the string of pocketed coil springs, and means for causing relative movement between the string of pocketed coil springs and the plurality of adhesive applicators, along a longitudinal axis of the string. The apparatus is adapted to apply adhesive to the string of pocketed coil springs, during relative movement between the first string of pocketed coil springs and the plurality of adhesive applicators, in a pattern that varies between at least some pockets of the string of pocketed coil springs.

This invention relates to methods and apparatus for use in the manufacture of innerspring assemblies, in particular innerspring assemblies for mattresses or the like, said innerspring assemblies comprising strings of pocketed coil springs arrange side by side and adhered together laterally by adhesive.

It is well known to assemble innerspring assemblies for mattresses and the like from pocketed coil springs. Typically, strings of pocketed coil springs are manufactured by feeding the springs directly from a spring coiling machine into the space between two plies of a weldable fabric, the two plies then being sealed together to form pockets which encapsulate the springs. The fabric is then indexed forward, the next spring(s) encapsulated, and so on. In this way, lengthy strings of pocketed coil springs are built up. An innerspring assembly of appropriate dimensions for a mattress can then be built up by placing appropriate lengths of pocketed coil springs, commonly referred to as strings, side by side and adhering them together, eg with adhesive. Automated methods for forming innerspring assemblies in this way, and apparatus for carrying out such methods, are known.

Sometimes it is desirable for the firmness of the innerspring assembly to vary along its length. For instance, it is known to manufacture a mattress with three zones of firmness, the central region, which carries the greatest part of the weight of a person lying on the mattress, being relatively stiff, with the head and foot parts of the mattress being less stiff for greater comfort. A more sophisticated arrangement is a five zone mattress in which the central part is again the stiffest, but the extreme ends are also somewhat stiffer than the intermediate regions. The manufacture of mattresses having a plurality of zones of varying stiffness, each zone being intended to support a different portion of the user's body, is well known in the art. See, for example, published International patent application WO00/55088.

This variation in the firmness is typically achieved by producing strings of pocketed coil springs that are arranged across the width of the innerspring assembly, and either varying the quantity of adhesive used to join adjacent strings, between different zones of the innerspring assembly, or varying the firmness of the springs used in the strings that form the different zones. However, these methods suffer from the significant disadvantage that the use of strings of pocketed coil springs that will be arranged across the width of the innerspring assembly requires more strings to be produced for each innerspring assembly, relative to the use of longitudinally arranged strings, which makes these methods inefficient.

WO 00/55088, a published International patent application, discloses a method in which each string of pocketed coil springs is positioned beneath a plurality of adhesive applicators, such that each applicator is aligned with a particular pocket. Each applicator deposits adhesive onto the pocket with which it is aligned. A variation in the firmness of the innerspring assembly may achieved using longitudinally arranged strings of pocketed coil springs by varying the quantity of adhesive applied along the length of the string.

However, the method disclosed by WO 00/55088 suffers from the disadvantage that large quantities of adhesive may be required to achieve a significant difference in firmness between zones. This can cause excessive restriction of axial deformation of the springs, and hence may excessively reduce the spring action of the mattress in those areas. Furthermore, this method requires a rack of adhesive applicators, which must be at least as long as the string of pocketed coil springs, and must have a separation between the adhesive applicators that is equal to the separation between the centres of the pocketed coil springs. The rack of adhesive applicators may therefore be expensive to manufacture, and may be difficult to modify between different configurations of strings.

There have now been devised methods and apparatus for use in the manufacture of innerspring assemblies, which overcome or substantially mitigate the above-mentioned or other disadvantages of the prior art.

According to a first aspect of the invention, there is provided a method of applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which method comprises the steps of

(a) providing apparatus for applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which apparatus comprises a plurality of independently actuatable adhesive applicators, each having a different transverse position relative to a longitudinal axis of the string of pocketed coil springs;

(b) causing relative movement between the string of pocketed coil springs and the plurality of adhesive applicators, along a longitudinal axis of the string; and

(c) applying adhesive to the string of pocketed coil springs, during relative movement between the first string of pocketed coil springs and the plurality of adhesive applicators, in a pattern that varies between at least some of the pockets of the string of pocketed coil springs.

According to a further aspect of the invention, there is provided apparatus for applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which apparatus comprises a plurality of independently actuatable adhesive applicators, each having a different transverse position relative to a longitudinal axis of the string of pocketed coil springs, and means for causing relative movement between the string of pocketed coil springs and the plurality of adhesive applicators, along a longitudinal axis of the string, wherein the apparatus is adapted to apply adhesive to the string of pocketed coil springs, during relative movement between the first string of pocketed coil springs and the plurality of adhesive applicators, in a pattern that varies between at least some pockets of the string of pocketed coil springs.

The method and apparatus according to the invention are advantageous principally in that adhesive is applied in a pattern that varies between at least some pockets of the string of pocketed coil springs, during relative movement between the string of pocketed coil springs and the plurality of adhesive applicators. This enables the firmness of the resultant innerspring assembly, which is formed by a plurality of strings placed side-by-side and adhered together by the applied adhesive, to vary in the direction along which the strings of pocketed coil springs are orientated, and hence enables zoned innerspring assemblies to be manufactured more efficiently than in the prior art. Furthermore, the apparatus has a simpler construction, and the method requires less complex control, relative to prior art methods and apparatus that utilise more than one adhesive applicator.

In preferred embodiments, the adhesive applicators are disposed on a linear axis, which is preferably aligned with the operable axis, ie the normal compression axis, of the coil springs of the string to which adhesive is being applied. This normal compression axis is preferably orthogonal to the longitudinal axis of the string. These features allow the apparatus to be a simple arrangement for applying adhesive to a plurality of points on spring pockets in a string. The apparatus is less costly to manufacture and operate than prior art apparatuses having more complex arrangements of applicators.

In preferred embodiments, the string of pocketed coil springs may be moved relative to the adhesive applicators, or vice versa, during actuation of the adhesive applicators. In presently preferred embodiments, the string of pocketed coil springs is moved relative to the adhesive applicators, which are preferably stationary relative to the remainder of the apparatus during application of adhesive to the string. This feature is advantageous as the extra parts and programming needed to enable the applicators to move relative to the remainder of the apparatus are not required. The feature therefore results in an apparatus which is less complex than the prior art apparatuses.

The string of pocketed coil springs may be fed past the adhesive applicators, such that when the entire string is located beyond the adhesive applicators, adhesive has been applied to the length of the string.

According to further aspects of the invention, there is provided a method and an apparatus for manufacturing an innerspring assembly, such as a mattress, which comprise the method and/or apparatus described above for applying adhesive to a string of pocketed coil springs. The method according to the invention preferably therefore includes a step of (d) bringing a second string of pocketed coil springs into contact with a first string of pocketed coil springs, with adhesive having been applied to at least one of those strings. Typically, adhesive has already been applied to the second string of pocketed coil springs before it is brought into contact with the first string of pocketed coil springs. Most preferably, steps (b), (c) and (d) are repeated for further strings of pocketed coil springs, so as to form an innerspring assembly comprising strings of pocketed coil springs arranged side-by-side, with adhesive acting between abutting surfaces of adjacent strings of pocketed coil springs.

The apparatus according to the invention preferably therefore includes means for bringing a second string of pocketed coil springs into contact with a first string of pocketed coil springs, with adhesive having been applied to at least one of those strings. Typically, the apparatus is adapted to apply adhesive to the second string of pocketed coil springs before it is brought into contact with the first string of pocketed coil springs. The apparatus most preferably includes means for successively bringing a string to which adhesive has been applied into contact with the preceding string to which adhesive has been applied, in order to form an innerspring assembly comprising strings of pocketed coil springs arranged side-by-side, with adhesive acting between abutting surfaces of adjacent strings of pocketed coil springs.

It has been found that the separation between a weight-bearing face of the innerspring assembly, and the adhesive acting between abutting surfaces of adjacent strings of pocketed coil springs, at least partially determines the firmness of that part of the weight-bearing face that is defined by those pockets. In particular, the less the separation between the weight-bearing face and the adhesive applied to an abutting surface of a particular pocketed coil spring, the greater the firmness of that part of the weight-bearing face that is defined by that pocketed coil spring. This is because the adhesive acts to transfer a force applied to a first pocketed coil spring onto a second pocketed coil spring bonded to it. Therefore, the closer to the end of the first pocketed coil spring the adhesive is located, the earlier in the stage of compression of the first pocketed coil spring is the point at which the force begins to be transferred. This results in an increased resultant stiffness.

For this reason, adhesive is preferably applied to the string of pocked coil springs in a pattern that has a plurality of zones, with the separation between the adhesive and the weight-bearing face(s) of the innerspring assembly being different between at least some of the zones.

Each string of pocketed coil springs is preferably generally conventional. In particular, each string of pocketed coil springs generally comprises a series of fabric pockets, each pocket enclosing a coil spring. The operable axes of the springs are generally all orientated in the same direction, which is preferably orthogonal to the longitudinal axis of the string. The ends of the coil springs are preferably aligned in a common plane, on at least one major side, and most preferably on both major sides, of the innerspring assembly, thereby defining the weight-bearing surface(s). Adhesive is therefore applied to a side surface of each string of pocketed coil springs, such that the strings are arranged side-by-side in the innerspring assembly. The pockets are generally dimensioned such that the springs are at least partially compressed in a rest configuration of the innerspring assembly. Each pocket is typically generally cylindrical in shape.

The adhesive applicators are preferably arranged to apply adhesive to each pocketed coil spring in turn, with adhesive being applied to a particular pocketed coil spring before any adhesive is applied to the next pocketed coil spring to which adhesive is to be applied. Hence, the plurality of adhesive applicators are preferably arranged to apply adhesive to a single pocket at the same time. The relative movement between the string of pocketed coil springs and the plurality of adhesive applicators may be indexed movement, such that each pocket is brought into alignment with the plurality of applicators in turn. However, the relative movement is preferably continuous, and most preferably of substantially constant speed, over a plurality of pocketed coil springs, and most preferably over the majority, or all, of the string.

Returning to the arrangement of adhesive applicators, the adhesive applicators may be disposed in mutually fixed relation, or may indeed be movable either before, or during use, for example transversely relative to the longitudinal axis of the string.

The adhesive from each adhesive applicator may be applied as a continuous line of adhesive that extends over a plurality of pocketed coil springs. Alternatively, the adhesive may be applied as discrete deposits of adhesive on each pocketed coil spring to which adhesive is applied. Where more than one discrete deposit of adhesive is applied to a pocketed coil spring, the deposits of adhesive are preferably aligned with a central axis of the pocketed coil spring when it is desired to form an innerspring assembly in a square array. In alternative embodiments, the deposits of adhesive are preferably offset from a central axis of the pocketed coil spring when it is desired to form an innerspring assembly in a nested arrangement, ie in which the pockets are arranged in hexagonal array.

In presently preferred embodiments, the string of pocketed coil springs is moved by means of one or more conveyors, for example a conveyor on each side of the string, between which the string is held by its pocketed coil springs being tensioned between the conveyors.

The string that is fed past the adhesive applicators may have already been cut to a desired length for incorporation into the innerspring assembly. Alternatively, the string may be cut to length once it has had adhesive applied. A further, presently preferred alternative is that the string is cut to a desired length following application of adhesive to some, but not all, of the pocketed springs. In this embodiment, the relative movement between the string and the adhesive applicators is stopped after only some of the pocketed springs have passed the adhesive applicators. The string is then cut. Once the string has been cut, relative movement between the string and the adhesive applicators is resumed. Once the relative movement between the string and the adhesive applicators has resumed, adhesive is applied to the remaining pocketed springs of the string.

In presently preferred embodiments, the adhesive applicators are disposed above the string of pocketed coil springs. Each adhesive applicator preferably has a downwardly directed outlet for transferring adhesive onto the surface of the string. As discussed above, the plurality of adhesive applicators are preferably arranged to apply adhesive to a single pocket at the same time. In one embodiment, the adhesive applicators are disposed on a linear axis, which is preferably aligned with the operable axis, ie the normal compression axis, of the coil springs of the string to which adhesive is being applied, which is preferably orthogonal to the longitudinal axis of the string.

The apparatus preferably includes at least one adhesive applicator adapted to apply adhesive to a substantially central region of one or more of the pocketed coil springs, and at least one adhesive applicator adapted to apply adhesive to a region of the same pocketed coil spring(s) that is closer to an end of the pocket, and hence closer to a weight-bearing surface of the innerspring assembly, than the central region. In presently preferred embodiments, where the innerspring assembly has weight-bearing surfaces on each side of the assembly, the apparatus preferably includes a further adhesive applicator adapted to apply adhesive to a region of the same pocketed coil spring(s) that is closer to the other end of the pocket, and hence closer to the other weight-bearing surface of the innerspring assembly, than the central region.

The apparatus may therefore be provided with three adhesive applicators. However, the apparatus may be provided with more than three applicators in the event that more variation of firmness is required. In addition, or alternatively, each adhesive applicator may have more than one outlet nozzle, in order to achieve a greater spread of adhesive from each applicator.

The actuation of the adhesive applicators is preferably controlled by a pre-programmed microprocessor or the like. Where three adhesive applicators are provided, depositing adhesive onto a pocketed coil spring preferably involves the actuation of either the central applicator alone, the outer two applicators only, or all three applicators. However, any combination of applicators may be actuated as desired. Where more than one applicator is actuated, adhesive is preferably dispensed from each of the applicators simultaneously, or substantially simultaneously, onto a particular pocket.

According to a further aspect of the invention, there is provided an innerspring assembly manufactured by the method and/or apparatus described above.

As discussed above, the innerspring assembly may comprise strings of pocketed coil springs that are adhered together, side-by-side, with adhesive that is disposed in a pattern that has a plurality of zones, with the separation between the adhesive and the weight-bearing face(s) of the innerspring assembly being different between at least some of the zones. This arrangement provides zones of the weight-bearing face(s) of the innerspring assembly that have different firmnesses. In presently preferred embodiments, the strings of pocketed coil springs will be arranged longitudinally, ie along the length, of the innerspring assembly, such that the firmness of the weight-bearing face(s) varies along the length of the innerspring assembly.

The present invention is particularly advantageous in that it also enables a variation in firmness across the width of the innerspring assembly by using different forms of springs, eg different wire or spring diameters, in different strings of pocketed coil springs that form the innerspring assembly. In particular, it is common for mattresses with “his and hers” sides to be formed by joining two smaller mattresses with different firmnesses together. The present invention enables a zoned mattress to be formed with “his and hers” sides by using a different form of spring for the strings of pocketed coil springs on one side of the innerspring assembly, relative to the form of spring used for the strings of pocketed coil springs on the other side of the innerspring assembly.

The apparatus according to the invention preferably also includes a coiling assembly for forming the coil springs of the innerspring assembly, and preferably also an encapsulation assembly in which coil springs are inserted between juxtaposed sheets of material, and in which the sheets of material are joined together to form pockets that each encapsulates a coil spring. Each of these assemblies is preferably disposed prior to the assembly for applying adhesive to a string of pocketed coil springs. In the encapsulation assembly, each coil spring is preferably fed into the space between two plies of a weldable fabric, the two plies then being sealed together to form pockets which encapsulate the coil springs. The fabric is preferably then indexed forward, the next spring(s) encapsulated, and so on, so as to form a continuous string of pocketed coil springs. The continuous string of pocketed coil springs may then be severed to form separate strings of pocketed coil springs.

A further advantage of the invention is that it enables mattresses having a “Virtual Frame” to be constructed in a simple, low-cost way. If the peripheral regions of a mattress are generally stiffer than their neighbouring regions, they provide a “Virtual Frame”. Such a mattress can be produced using the present invention by, for example, using a larger quantity of adhesive to connect each spring pocket lying in a peripheral region of the assembly, relative to its neighbouring spring pocket in the transverse direction. This can be achieved, for example, by applying a larger quantity of adhesive to one or more of those strings in peripheral regions of the assembly that are orientated parallel to the boundaries of the assembly, eg along the length of these strings, and also to the spring pockets located in end regions of one or more of the intermediate strings.

The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which

FIG. 1 is a schematic plan view of apparatus in accordance with the invention, during use;

FIG. 2 is a schematic and fragmentary, perspective view of apparatus in accordance with the invention, during use;

FIG. 3 is a cross-sectional view along the line III-III in FIG. 1;

FIGS. 4 a and 4 b are schematic side views of strings of pocketed coil springs, to which different patterns of adhesive have been applied, which are both suitable for use in the manufacture of a “3-zone”mattress;

FIG. 5 is a fragmentary plan view of a nested innerspring assembly; and

FIG. 6 is a fragmentary side view of a string of pocketed coil springs having a pattern of adhesive suitable for assembly of a mattress having a nested spring configuration.

FIG. 1 is a schematic plan view of apparatus 1 in accordance with the invention for the manufacture of an innerspring assembly. The apparatus is fed with a continuous chain 2 of pocketed coil springs 3, which may be manufactured by conventional techniques.

The chain 2 of pocketed coil springs 3, which has not yet been cut into strings of the desired length for incorporation in the innerspring assembly, is transported from left to right in FIG. 1 by a paddle wheel (not shown). This causes the chain 2 of pocketed coil springs 3 to be received between two conveyor belts 41. The conveyor belts 41 extend parallel to each other and have opposing conveying surfaces. The separation of the conveyor belts 41 is such that when the chain 2 of pocketed coil springs 3 enters the gap between the belts 41, the conveying surfaces co-operate to hold the chain 2 of pocketed coil springs 3 in compression, each conveying surface engaging the ends of the pocketed coil springs 3 of the chain 2. The conveyor belts 41 convey the chain 2 of pocketed coil springs 3 longitudinally, causing it to pass underneath the applicator assembly 5.

The applicator assembly 5 is adapted to dispense a quantity of adhesive 30 onto the outer surface of each pocket 3 of the chain 2. The applicator assembly 5 is shown in more detail in FIG. 2. The applicator assembly 5 comprises a support 25 and three adhesive applicators: a left-hand adhesive applicator 7 a, a central adhesive applicator 7 b and right-hand adhesive applicator 7 c. The adhesive applicators 7 a, 7 b, 7 c are referred to collectively below by the reference numeral 7. Each of the applicators 7 is connected to a supply of adhesive (not shown). In addition, each of the applicators 7 is connected to the support 25 and depends downwardly therefrom, such that they are capable of applying adhesive 30 to the surface of a pocket 3 located directly beneath the applicator assembly 5.

The applicators 7 are disposed in a spaced apart and linear configuration on the support 25, such that the applicators 7 are able to apply adhesive 30 to locations along the central axis of the spring pocket 3. In this way, actuation of the central applicator 7 b causes adhesive to be deposited on a central region of the surface of the pocket 3, while actuation of one of the applicators 7 a, 7 c located either side of the central applicator 7 b causes adhesive 30 to be deposited at a location which is closer to the ends of the spring pocket 3.

As the chain 2 moves longitudinally, the applicators 7 are actuated in order to deposit a quantity of adhesive 30 onto the surfaces of the pockets 3 in turn.

Once a number of pockets 3 of the chain 2 have passed underneath the applicator assembly 5, the chain 2 is brought to rest. At this point, the device 40 applies two parallel ultrasonic welds at a location on the chain 2. The welds are located between two spring pockets 3 and are orientated in a direction roughly perpendicular to the direction of transport of the chain 2. The device 40 is also provided with a cutting tool. Once the device 40 has applied the ultrasonic welds, it uses the cutting tool to cut the chain 2 between the two welds, causing a string 6 of pockets to be separated from the remainder of the chain 2. The conveyor belts 41 then transport the string 6 longitudinally, causing the remaining pockets 3 of the string 6 to pass underneath the applicator assembly 5 and receive adhesive. FIG. 1 shows the apparatus at a time when all of the pockets 3 of the string 6 have passed under the applicator assembly 5.

FIG. 2 gives a schematic impression of the apparatus 1 immediately after the applicators 7 have deposited adhesive 30 onto a pocket 3 b. The applicators 7 are located above a particular pocket 3 b, which is part of the string 6 of pocketed coil springs. Only three pockets of the string 6 are shown in FIG. 2, specifically 3 a, 3 b and 3 c. The arrow A indicates the direction of travel of the string 6. FIG. 2 shows the apparatus after the applicators 7 have deposited adhesive 30 onto spring pockets 3 a and 3 b. When the first of the pockets 3 a was located under the applicators 7, only the central applicator 7 b was actuated, hence adhesive 30 was deposited only in one, central, location on the pocket 3 a. When the second pocket 3 b was located under the applicators 7, all three of the applicators 7 were actuated, depositing adhesive 30 onto the pocket 3 b in three locations as shown. It will be appreciated that the number of applicators 7 actuated in respect of each pocket is variable and is software controlled. Any of the applicators 7 may be actuated either alone, or in combination with one or both of the other applicators 7.

As shown in FIG. 2, the adhesive is applied as a continuous line of adhesive, which may extend across a number of pockets of the string 6. This is the simplest arrangement to manufacture, and enables the pocketed coil springs to be adhered together in either a square or hexagonal array in the innerspring assembly. Alternatively, however, it is possible to apply discrete deposits of adhesive to each pocket, as discussed in more detail below.

FIG. 3 shows a schematic cross-sectional view of the arrangement of FIG. 1 along the line III-III. Once the whole of the length of the string 6 has been transported past the applicator assembly 5, the string 6 is brought to rest. At this point, a hydraulic ram 42, located beneath the string 6 is actuated. This causes a transport plate 8 to engage the underside of the string 6, transporting the string 6 upwards into a chute 43. Previously processed strings 6 a, 6 b are located in the chute 43. Moving the string 6 upwardly causes the side of the string 6 to which adhesive has recently been applied to engage the underside of a previously processed string 6 a. This adheres the two strings 6, 6 a together and causes the previously processed strings 6 a, 6 b to move along the chute 43.

The next string is then processed in the same manner as the preceding string 6. In this manner, the completed innerspring construction is built up from successive strings, and removed from the other end of the chute 43.

The degree of adhesion between adjacent pockets in successive strings 6 in the innerspring assembly determines the degree of firmness of that part of the innerspring assembly. It is thus possible to control the firmness of the mattress by appropriate application of adhesive 30 to the respective pockets.

FIGS. 4 a and 4 c show two different patterns of adhesive application, each appropriate for a so-called “3-zone” mattress, the pattern of FIG. 4 a having continuous lines of adhesive, and the pattern of FIG. 4 c having discrete deposits of adhesive aligned with the central axis of each pocket, and hence suitable for use in assembly of a square array of pocketed coil springs. Adhesive 30 is applied in the manner described above to a number of different strings 6, the adhesive patterns being that shown in FIG. 4 a or 4 c. The strings 6 are pressed together to form a mattress such that each string 6 extends longitudinally from the head to the foot of the mattress. Thus, the “head” and “foot” regions of the mattress comprise pocket springs linked to each other by adhesive 30 deposited by the central applicator 7 b only, as shown by the deposits 13 of adhesive 30 located centrally on the spring pockets 3 in the end portions 20 and 22 of the strings 6 in FIGS. 4 a and 4 c. In the central part of the mattress, however, the pockets are linked by adhesive 30 deposited by all three applicators 7, as shown by the three different deposits 18 located on the pockets in the middle portion 21 of the strings in FIGS. 4 a and 4 c. In such a construction, the head and foot regions of the mattress are relatively soft, while the central region of the mattress is relatively firm.

FIG. 4 b shows a different pattern of adhesive application, which is also appropriate for a so-called “3-zone” mattress. As in FIG. 4 a, the pattern of FIG. 4 b has continuous lines of adhesive. However, it differs from the pattern of FIG. 4 a in that only applicators 7 a and 7 c, which are located on either side of the central applicator 7 b, are used to deposit adhesive onto the spring pockets in the central part of the string 21.

The pattern of adhesive application shown in FIG. 4 c is appropriate for innerspring assemblies in which the pocketed coil springs are arranged in a square array. Another arrangement, which is sometimes used, is a so-called nested arrangement, in which the spring pockets are arranged in a hexagonal array. Such an array is shown in FIG. 5. In the formation of such an array, it is not the central part of each spring pocket which is pressed against the pockets of the previous string, but rather surfaces of the pocket which are offset from the centre line. FIG. 6 shows an example of an adhesive pattern that would be appropriate for such a nested arrangement. In this pattern, the adhesive is applied to the pockets at locations along lines parallel to, but offset from, the centre line of the pocket. As can be seen in FIG. 6, the adhesive 30 can be applied by all three applicators 7, as shown at 18, or by the central applicator 7 b only, as shown at 13. 

1. An apparatus for applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which apparatus comprises: a plurality of independently actuatable adhesive applicators, each having a different transverse position relative to a longitudinal axis of the string of pocketed coil springs; and means for causing relative movement between the string of pocketed coil springs and the plurality of adhesive applicators, along a longitudinal axis of the string, wherein the apparatus is adapted to apply adhesive to the string of pocketed coil springs, during relative movement between the first string of pocketed coil springs and the plurality of adhesive applicators, in a pattern that varies between at least some pockets of the string of pocketed coil springs.
 2. The apparatus as claimed in claim 1, wherein the adhesive applicators are disposed on a linear axis, which is aligned with an operable axis of the coil springs of the string.
 3. The apparatus as claimed in claim 1, wherein the apparatus is adapted to move the string of pocketed coil springs relative to the adhesive applicators, which are stationary relative to a remainder of the apparatus, during application of adhesive to the string.
 4. The apparatus as claimed in claim 1, wherein the apparatus is adapted to apply adhesive to the string of pocked coil springs in a pattern that has a plurality of zones, with a separation between the adhesive and weight-bearing faces of the resultant innerspring assembly being different between at least some of the zones.
 5. The apparatus as claimed in claim 1, wherein the adhesive applicators are arranged to apply adhesive to each pocketed coil spring in turn, with adhesive being applied to a particular pocketed coil spring before any adhesive is applied to a next pocked coil spring to which adhesive is to be applied.
 6. The apparatus as claimed in claim 5, wherein the adhesive applicators are arranged to apply adhesive to a single pocket at the same time.
 7. The apparatus as claimed in claim 1, wherein the relative movement between each string of pocketed coil springs and the plurality of adhesive applicators is continuous during application of adhesive to the string.
 8. The apparatus as claimed in claim 1, wherein the adhesive applicators are disposed in mutually fixed relation.
 9. The apparatus as claimed in claim 1, wherein the apparatus is adapted to move the adhesive applicators relative to the string of pocketed coil springs, which are stationary relative to a remainder of the apparatus, during application of adhesive to the string.
 10. The apparatus as claimed in claim 1, wherein the apparatus includes at least one adhesive applicator adapted to apply adhesive to a substantially central region of one or more of the pocketed coil springs, and at least one adhesive applicator adapted to apply adhesive to a region of the same pocketed coil springs that is closer to an end of the pocket, and hence closer to a weight-bearing surface of the resultant innerspring assembly, than the central region.
 11. The apparatus as claimed in claim 10, wherein the apparatus includes a further adhesive applicator adapted to apply adhesive to a region of the same pocketed coil springs that is closer to the other end of the pocket, and hence closer to the other weight-bearing surface of the innerspring assembly, than the central region.
 12. The apparatus as claimed in claim 1, wherein each adhesive applicator has more than one outlet nozzle.
 13. A method of applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which method comprises the steps of (a) providing apparatus for applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly, which apparatus comprises a plurality of independently actuatable adhesive applicators, each having a different transverse position relative to a longitudinal axis of the string of pocketed coil springs; (b) causing relative movement between the string of pocketed coil springs and the plurality of adhesive applicators, along a longitudinal axis of the string; and (c) applying adhesive to the string of pocketed coil springs, during relative movement between the first string of pocketed coil springs and the plurality of adhesive applicators, in a pattern that varies between at least some of the pockets of the string of pocketed coil springs.
 14. The method as claimed in claim 13, wherein the adhesive applicators are disposed on a linear axis, which is aligned with an operable axis, which is a normal compression axis, of the coil springs of the string to which adhesive is being applied.
 15. The method as claimed in claim 13, wherein the string of pocketed coil springs is moved relative to the adhesive applicators, which are stationary relative to a remainder of the apparatus during application of adhesive to the string.
 16. The method as claimed in claim 13, wherein the apparatus for applying adhesive to a string of pocketed coil springs during manufacture of an innerspring assembly is the apparatus claimed in claim
 1. 17. The method as claimed in claim 13, wherein the adhesive is applied to the string of pocked coil springs in a pattern that has a plurality of zones, with the separation between the adhesive and weight-bearing faces of the innerspring assembly being different between at least some of the zones.
 18. The method as claimed in claim 13, wherein adhesive is applied to each pocketed coil spring in turn, with adhesive being applied to a particular pocketed coil spring before any adhesive is applied to the next pocked coil spring to which adhesive is to be applied.
 19. The method as claimed in claim 13, wherein a relative movement between the string of pocketed coil springs and the plurality of adhesive applicators is continuous during application of adhesive to the string.
 20. The method as claimed in claim 13, wherein the adhesive from each adhesive applicator is applied as a continuous line of adhesive that extends over a plurality of pocketed coil springs.
 21. The method as claimed in claim 13, wherein the adhesive applicators are moved relative to the string of pocketed coil springs, which are stationary relative to the remainder of the apparatus, during application of adhesive to the string.
 22. An apparatus for manufacturing an innerspring assembly, which apparatus comprises the apparatus as claimed in claim 1 for applying adhesive to a string of pocketed coil springs.
 23. The apparatus as claimed in claim 22, wherein the apparatus includes means for bringing a second string of pocketed coil springs into contact with a first string of pocketed coil springs, with adhesive having been applied to the second string of pocketed coil springs before it is brought into contact with the first string of pocketed coil springs.
 24. The apparatus as claimed in claim 23, wherein the apparatus includes means for successively bringing a string to which adhesive has been applied into contact with the preceding string to which adhesive has been applied, in order to form an innerspring assembly comprising strings of pocketed coil springs arranged side-by-side, with adhesive acting between abutting surfaces of adjacent strings of pocketed coil springs.
 25. A method for manufacturing an innerspring assembly, which method comprises the method as claimed in claim 13 for applying adhesive to a string of pocketed coil springs.
 26. The method as claimed in claim 25, further comprising: (d) bringing a second string of pocketed coil springs into contact with a first string of pocketed coil springs, with adhesive having already been applied to the second string of pocketed coil springs before it is brought into contact with the first string of pocketed coil springs.
 27. The method as claimed in claim 26, wherein the steps (b), (c) and (d) are repeated for further strings of pocketed coil springs, so as to form an innerspring assembly comprising strings of pocketed coil springs arranged side-by-side, with adhesive acting between abutting surfaces of adjacent strings of pocketed coil springs.
 28. The method as claimed in claim 25, wherein the innerspring assembly is formed with strings of pocketed coil springs that are adhered together, side-by-side, with adhesive that is disposed in a pattern that has a plurality of zones, with the separation between the adhesive and weight-bearing faces of the innerspring assembly being different between at least some of the zones.
 29. The method as claimed in claim 28, wherein the strings of pocketed coil springs are arranged longitudinally of the innerspring assembly, such that the firmness of the weight-bearing faces varies longitudinally of the innerspring assembly.
 30. The method as claimed in claim 29, wherein a variation in firmness across the width of the innerspring assembly is provided by different forms of springs being present in different strings of pocketed coil springs that form the innerspring assembly.
 31. The method as claimed in claim 30, wherein a different form of spring is present in the strings of pocketed coil springs on one side of the innerspring assembly, relative to the form of spring present in the strings of pocketed coil springs on the other side of the innerspring assembly.
 32. An innerspring assembly manufactured by the method as claimed in claim 25, or using the apparatus as claimed in claim
 22. 33. The innerspring assembly as claimed in claim 32, wherein the innerspring assembly comprises strings of pocketed coil springs that are adhered together, side-by-side, with adhesive that is disposed in a pattern that has a plurality of zones, with the separation between the adhesive and the weight-bearing faces of the innerspring assembly being different between at least some of the zones.
 34. The innerspring assembly as claimed in claim 33, wherein the strings of pocketed coil springs are arranged longitudinally of the innerspring assembly, such that the firmness of the weight-bearing faces varies longitudinally of the innerspring assembly.
 35. The innerspring assembly as claimed in claim 34, wherein a variation in firmness across the width of the innerspring assembly is provided by different forms of springs being present in different strings of pocketed coil springs that form the innerspring assembly.
 36. The innerspring assembly as claimed in claim 35, wherein a different form of spring is present in the strings of pocketed coil springs on one side of the innerspring assembly, relative to the form of spring present in the strings of pocketed coil springs on the other side of the innerspring assembly. 